Inorg. Chem. 1980, 19, 1356-1365
1356
The 300 and 0 K volume susceptibilities as corrected for core diamagnetism are shown in Table 111. Figure 10 shows the values plotted as functions of composition together with corresponding values of T,. It is remarkable that both xv(O K) and T, exhibit the same composition dependence. Pauli susceptibility, in general, is intimately related to the band structure of a compound. In the presence of complicated structure in the band, the 0 K Pauli volume susceptibility would be proportional to the density states at the Fermi level N(eF). Figure 10 indicates that T, in these compounds depends strongly on N(eF),as would be in qualitative agreement with the simple BCS theory prediction (eq 3). Tc (u)exp[-l/(N(€F))V] The fact that T, and N(cF)are similarly dependent on c/a is puzzling. No immediate connection between c / a and N(eF)
is apparent. Overlap between unit cells should depend on aH alone, as is evident from S ~ M O ~ SMore ~ - ~detailed .~ bandstructure calculations are needed to elucidate the relationship of T,, cia, and the susceptibility. By way of summary, we have presented evidence for ordering of chalcogens in P ~ M O ~ ( S ~ - , S ~with , . ) ~ respect to general- and special-position sites. The superconducting transition temperatures were found to be a linear function of c/a until selenium atoms substantially occupy the specialposition sites. The 0 K volume susceptibility exhibits the same composition dependence as T,, suggesting variations in T, reflect changes in the density of states at the Fermi level. The manner in which c / a and N(tF) are connected is unclear; it needs to be investigated in more detail. Registry No. PbMo6Ss, 39432-49-0; PbMo6Ses, 62462-65-1.
Contribution from the Institute of Inorganic and Analytical Chemistry and the Institute of Crystallography, University of Lausanne, CH-1005 Lausanne, Switzerland
Study of PtX2(PRJ2 in the Presence of PR3 in CH2C12Solution and the Cis-Trans Isomerization Reaction As Studied by 31P NMR. Crystal Structure of [PtCl(PMe3)3]Cl ROLAND FAVEZ,'"sb RAYMOND ROULET,*Ia ALAN A. PINKERTON,ic and DIETER SCHWARZENBACH'C Received May 18, 1979 The identity of the species present in dichloromethane solutions of PtX2L2and L (L = PMe3, PEt,, P-n-Bu3, P(tol), where to1 = p-tolyl; Pt:L ratios from 1:0.05 to 1:5) are cis- and trans-PtX2Lz, [PtXL3]' (X = CI, Br), and [PtXL4]' (X = C1, Br, I; L = PMe?). The only species with three coordinated phosphines which is five-coordinate in solution is PtI,(PMe?),, whose IR and NMR parameters are consistent with a square-pyramidal geometry having one phosphine in the apical position. All other "tris" complexes [PtXL3]+are four-coordinate in solution as shown by UV and "P NMR spectroscopy, and this geometry is also found in the solid state (IPtCI(PMe3)3JClX-ray crystal structure). The complexes [PtX(PMe3)4]t have a square-pyramidal geometry with X in the apical position. In the case of L = PMe,, 31PNMR studies show that intermolecular phosphine exchange occurs between [PtC1L3]', [PtClL,]', Pt12L3,and free L, whose activation parameters, estimated from line-shape analysis, are reported. Contrary to previous reports, chloride ion is found to displace one phosphine from [PtC1L3]+ ion, giving the cis-PtC12L2isomer in a fast step prior to cis-trans equilibration. The results indicate that the cis-trans isomerization of PtX2L2catalyzed by L proceeds by rapid displacement of X- by L followed by slow displacement of L by X- and not by pseudorotation of a five-coordinate intermediate. A similar mechanism was established for the isomerization of the alkyl complex PtC1(CH2CN)(PPh3)2.
Introduction Since the original proposal by Bas010 and Pearson2 of the double displacement mechanism for the phosphine-catalyzed cis-trans isomerization of tetragonal-planar platinum(I1) complexes, many studies3-18with conflicting results and in(a) Institut de Chimie Mingrale et Analytique. (b) Based, in part, on the Ph.D. thesis of R.F., Universitd de Lausanne. (c) Institut de Cristallnsranhie. ~
Basolo, F.; Pearson, R. G. "Mechanisms of Inorganic Reactions", 2nd ed.; Wiley: New York, 1967; p 424. Haake, P; Pfeiffer, R. M. J. Am. Chem. SOC.1970, 92, 4996. Haake, P.; Pfeiffer, R. M. Chem. Commun. 1969, 1330; J. Am. Chem. Soc. 1970, 92, 5243. Cooper, D. G.; Powell, J. J . Am. Chem. SOC.1973, 95, 1102. Cooper, D. G.; Powell, J. Can. J . Chem. 1973, 51, 1634. Louw, W. J. J . Chem. Soc., Chem. Commun. 1974, 353. Powell, J; Cooper, D. G. J . Chem. SOC.,Chem. Commun. 1974,149. Redfield, D. A.; Nelson, J. H. J. Am. Chem. SOC. 1974, 96, 6219. Redfield, D. A,; Nelson, J. H. Inorg. Chem. 1973, 12, 15. Verstuyft, A. W.; Nelson, J. H. Ibid. 1975, 14, 1501. Redfield, D. A.; Nelson, J. H.; Henry, R. A; Moore, D. W.; Jonassen, H . B. J . Am. Chem. SOC.1974, 96, 6298.
0020-1669/80/ 13 19-1356$01 .OO/O
t e r p r e t a t i ~ n s ~ have - ~ J ~appeared in the literature. The following mechanisms have been proposed to date: (a) a double displacement mechanism (eq 1) which implies phosphine excis-PtX2L2 +
fast
[PtXL31++x- slow trans-PtX2L2+ L (1)
change and an ionic intermediate from which X- is able to displace L (This mechanism is in agreement with the stereosDecific nature of all substitution reactions of platinum(I1) iomplexes observed so far.), (b) a pseudorotation mechanism (12) Redfield, D. A,; Cary, L. W.; Nelson, J. H. Inorg. Chem. 1975, 14, 50. (13) Verstuyft, A. W.; Cary, L. W.; Nelson, J. H. Inorg. Chem. 1976, 15, 3161. (14) Pfeiffer, R. M. Synth. React. Inorg. Met.-Org. Chem. 1976, 6, 55. (15) Louw, W. J. Inorg. Chem. 1977, 16, 2147. (16) Faraone, G.; Ricevuto, U.; Romeo, R.; Trozzi, M. J . Chem. SOC.A 1971, 1877. (17) Romeo, R.; Minniti, D.; Trozzi, M. Inorg. Chim. Acta 1975, 14, L15; Inorg. Chem. 1976, 15, 1134. Romeo, R. Ibid. 1978, 17,2040. (18) Jensen, K. A. Z . Anorg. Allg. Chem. 1936, 229, 225.
0 1980 American Chemical Society
PtX2(PR3)2in Presence of PR3 in CH2C12 (eq 2) proposed by Haake et ale3which implies a five-coor(2) cis-PtX2L2 + L’ F! PtX2L2L’ F! trans-PtX2L2+ L’ dinate transition state or intermediate (PtXzL2L’must be able to undergo a fluxional change which interconverts the position of L and X but not L and L’ during isomerization.), (c) the consecutive displacement of a neutral ligand by a neutral ligand (eq 3) proposed by Redfield and Nelsong where A and cis-PtX2L2 + L’ + PtX2L2L’ (A) PtX2LL’ + L e PtX2L’L2 (B) e trans-PtX2L2 + L’ (3)
Inorganic Chemistry, Vol. 19, No. 5, 1980 1357 Table I. The System PtX,(PMe,)2 and PMe, in CH,Cl, Solution [PMe3]added/[Pt]
trans-PtX,(PMe,), (x = Cl, Br)
traceb
cis-PtX,(PMe,), (>99%)
traceb 0.5c
trans-PtI,(PMe,), (>99%) cis-PtX,(PMe,), + [ PtX(PMe,),] (1 :1) [PtX(PMe,),l (>99%) [PtX(PMe,),l+ + [PtX(PMe,),] (1: 1) [PtX(PMe,),l (>99%) [PtX(PMe,),l+ + PMe, (1:8) trans-PtI,(PMe,), + PtI,(PMe,), (1:l) PtI,(F‘Me,), 0 9 9 % ) PtIz(PMe,), + [PtI(PMe,),l’ ( 1 : l ) [PtI(PMe,),l (>99%) [PtI(PMe,),]+ PMe, (1:3) +
1.oc 1.5d
*
B may be either transition states or intermediates and are not necessarily identical (These authors showed that there is phosphine mixing in these systems and that PtX2LL’ can be isolated in certain cases. They suggested that mechanism a should dominate in polar solvents when X- is poorly coordinating and L’ is a strong base, pathway b in nonpolar solvents when L and L’ have nearly the same basicity and are small, and pathway c in nonpolar solvents when X- is strongly coordinating.), (d) a dissociative mechanism (eq 4) proposed by cis-PtXRL2 e [PtRL2]+ + X- e trans-PtXRL2 (4)
species in soln
Starting Complex
+
+
2.0d 10d 0.5c 1.oc
1.9 2.0d 5.0e a Cis or trans. At 30 “C. CHClF, at -155 “C.
+
+
At -40 ‘C.
+
At -65 “C.
e
In
Romeo et a1.16 for the spontaneous isomerization of aryl- and Table 11. The System PtCl,L, and L in CH,Cl, Solution alkylplatinum(I1) complexes, which implies a dissociative step (L= PEt,, P-n-Bu,, P(tol),) generating a 14-electron species.” [LI added/ Arguments derived from the rate dependence on [L] are starting complex mi species in s o h at 30 “C useless since pathways a, b, and c will obey the same second-order rate law. Kinetic measurements with L # L’ are L = PEt, difficult to interpret since the thermodynamic stability of the cis- or trans-PtCl,L, trace cis- + trans-PtCl,L, (0.90:0.10) trans-PtClZL, + AgBF, 1.0 [PtClL,]+ + trans-PtCl,L, mixed-species PtX’LL’ must be taken into account. ‘H NMR (1 :0.80) (0.8:0. 2Ia spectroscopy is helpful, but temperature-dependent spectra for cis- or trans-PtCl,L, 3.0 [PtClLJ+ + L (1:2) most of these tertiary phosphine systems are superimposed non-first-order patterns intractable by line-shape analysis; e.g., L = P-n-Bu, cis- or trans-PtCl,L, trace cis- + @ans-PtCl,L, (0.92:0.08) see the conflicting discussions on the system PtX2(PPhMeJ2 trans-PtCl,L, 1.0 [PtClL,]+ + cis- + transPPhMeP5J5 Experimental investigation should concentrate Pta,L, + L (0.15:0.80:0.05: on the characterization of intermediates in solution by the most 0.85) direct method. For this reason, we have used 31PNMR trans-PtCl,L, 3.0 [PtClL,]+ + L (1:2) spectroscopy to examine the systems PtXzL2+ L (L = PMe3, L = P(tol), PEt,, P-n-Bu3, P(t01)~where to1 = p-tolyl) and report our cis- or trans-PtCl,L, trace cis- + trans-PtCl,L, (0.84:0.16) results herein, as well as the crystal structure of [PtCltrans-PtCl,L, + &NO, 1.0 [PtClL,]’ + [Pt(NO,)L,]+ (PMe3)3IC1. (1:l) (1:l) Results and Discussion trans-PtCl,L, 2.67 [PtClL,] + cis- + transPtCl,L, + L (0.20:0.84:0.16: 1. Studies of PtX2L2and L in Dichloromethane Solution 3.00) (L = PMe3, P E t , P-n-Bu3, P(t01)~). Identification of the a Species present prior to cis-trans equilibration. Species Present. The s y n t h e s i ~and ~ ~ ~spectral ’~ properties of cis- and trans-PtX2L2are well established (X = halide; L = coordinate ionic species, [PtXL3]+(L = PMe3,19PEt3, P-nPMe3,20-22PEt 3, 20-23,24 P - ~ - B u ~ ’ ~ , ’ ~ Cis-trans ). thermal B u , ~ ~or ) , as five-coordindte neutral PtX2L3(L = 2-phenylisomerization occurs in solution when a trace of L is added ph~sphindoline;~~ L = PPhMe2; X = Br, I).33 However no and the equilibrium thermodynamic parameters have been structure determination of these “tris” complexes has determined in benzene (L = PEt3,27 P-n-Pr3, P - ~ - B u ~ ~ ~ crystal ). been reported to date. Complexes with four (but none with Similar experiments have been carried out in various solvents five) bonded phosphines have been isolated in the solid state, for the palladium analogues PdX2L2 (L = PPh2Me, PPhMe2; e.g., [Pt(PMe3)4](BF4)2,20 and these “tetrakis” species in soX = Cl,29N330). Complexes with three bonded phosphines lution were invariably formulated as four-coordinate [PtL4]’+ have been isolated in the solid state and formulated as fourions, except for [PtH(PEt3)4]+34 and [Pt(alkyl)(PPhMe2)4]++.35 As the rate of cis-trans isomerization of PtX2L2(X = halide) Hartley, F. R. Organomet. Chem. Rev. 1970, 6, 126. is first order in both the complex and L, a knowledge of the Duddell, D. A.; Goggin, P. L.; Goodfellow,R. J.;Norton, M. G.;Smith, geometry and dynamic properties of species having more than J. G. J. Chem. SOC.A 1970, 545. Duddell, D. A.; Evans, J. G.; Goggin, P. L.; Goodfellow, R. J.; Rest, two bonded phosphines is crucial to a discussion of the isom-
+
+
A 1969, 2134. A. J.; Smith, J. G. J . Chem. SOC. Goggin, P. L; Goodfellow, R. J.; Haddock, S. R.; Knight, J. R.; Reed, F.J. S.;Taylor, B. F. J . Chem. Soc., Dalton Trans. 1974, 523. Grimm, S. 0.;Keiter, R. L.; McFarlane, W. Inorg. Chem. 1967, 6, 1133.
Pregosin, P. S.; Sze, Siu Ning. Helv. Chim. Acta 1978, 61,1878. Inorg. Synth. 1963, 7, 245. Pidcock, A.; Richards, R. E.; Venanzi, L. M. J . Chem. SOC.A 1966, 17117.
Chat;, J.; Wilkins, R. G. J . Chem. SOC.1952, 273. Chatt, J.; Wilkins, R. G. J . Chem. SOC. 1956, 525. Redfield, D. A,; Nelson, J. H. Inorg. Chem. 1973, 12, 15. Redfield, D. A.; Cary, L. W.; Nelson, J. H. Inorg. Chem. 1975, 14, 50.
(31) Church, M. J.; Mays, M. J. J . Chem. SOC. A 1968, 3074. (32) Collier, J. W.; Mann, F. G.: Watson, D. G.: Watson, H. R. J . Chem. SOC.1964, 1803. (33) Pearson, R. G.; Louw,W.; Rajaram, J. Inorg. Chim. Acta 1974, 9, 251. (34) English, A. D.; Meakin, P.; Jesson, J. P. J . Am. Chem. SOC. 1976,98,
.--.
677
(35) Favez, R. Thbe de doctorat, Universite de Lausanne, 1979. (36) Goggin, P. L.; Goodfellow,R. J.; Knight, J. R.; Norton, M. G.; Taylor, B. F. J . Chem. SOC., Dalton Trans. 1973, 2220. (37) Mather, G. G.; Pidcock, A.; Rapsey, G. J. N . J. Chem. Sac., Dalton Trans. 1973, 2095.
1358 Inorganic Chemistry, Vol. 19, No. 5, 1980
2 , 30
20
10
0
-10
-20
.30
-40 .50
-60
-70
Favez et al.
-80ppm
Figure 1. 31P(1H) FT NMR spectra in CD2C12at -40 ‘C of (a) a mixture of ~is-PtCl~(PMe,)~ and PMe, (1:1.05) and (b) [PtCl(PMe,) ,] C104 (asterisk: [PtC1(PMe,),] +).
XI
0
-20 -40 -60 -80 -100 -120 -140 -160 -180 200 ppm
Figure 3. 31P(’H) FT NMR spectra in CD2C12at -40 ‘C of (a) a mixture of tr~ns-PtI~(PMe~)~ and PMe3 (l:l), (b) Pt12(PMe3),,and (c) [PtI(PMe3)31PF6.
250
300 nm
250
300 nm
Figure 2. UV spectra in dichloromethane of (a) [PtCl(PMe3)3]CI at -30 and +30 ‘C and (b) [PtCl(PMe3),]C1O4([Pt] = 1.01 X lo4
0.5 -
M) .
erization mechanism. We have thus prepared a series of solutions of PtX,L, and L and compared their 31P(1HJ FT N M R spectra with those of known PtX2L2, [PtXL3]+,and [PtL4I2+complexes. The identity of the species present in dichloromethane solution is given in Table I for L = PMe, and in Table I1 for L = PEt,, P-n-Bu3, P(tol),. On the NMR time scale, intermolecular exchange at room temperature between PtX2L2and L (L = PMe,, PEt,, P-n-Bu,, P(tol),) and [PtXL,]’ and L (L = PEt3, P-n-Bu,, P(t01)~)is slow, but in the case of [PtX(PMe3),]+, [PtX(PMe3)4]C,or Pt12(PMe3), and free PMe3, a fast exchange is observed. In the latter case, the 31PN M R spectra were recorded at the low-temperature slow-exchange limit, and the spectral data of all observed species are summarized in Table 111. In all cases but one (L = PMe,; X = I), the “tris” species in solution are formulated as four-coordinate [PtXL3]+for the following reasons: (i) the 31PNMR spectrum of PtXzL2+ L (1:l) is identical with that of [PtXL3]Y (Y = Clod or PF,; e.g., Figure 1); (ii) the UV spectra of PtX2L, + L (1 :1) and of some isolated [PtXL3]X are identical with those of the corresponding [PtXL,]Y (e.g., Figure 2); (iii) the IR spectrum of [PtClL3]C1presents only one v(Pt-Cl) band in the solid state and in solution; (iv) there is no 35ClNMR evidence of contact ion pairing in CD2C12. The NMR spectrum of [PtCl(PMe3)3]C104at room temperature presents a single resonance attributable to the perchlorate anion whose width at half-height (4 Hz) is close to that of NaC10, in D20 (3 Hz). Stengle and Berman3*have shown that the formation of contact ion pairs broadens this resonance by a factor -lo2. For L = PMe,, the fast phosphine exchange precluded the observation of the characteristic 31PNMR pattern of [PtXL3]+at room tem-
perature (a doublet and a triplet, intensity ratio 2:l). However, the UV spectrum did not change between -30 and +30 OC (Figure 2). Thus, even for this system, no evidence was found for the hypothetical PtC12L3in dichloromethane solution. An X-ray diffraction study of [PtCl(PMe,),]Cl showed that this compound is also a four-coordinate complex in the solid state (vide infra). By contrast, Pt12(PMe3), is a five-coordinate complex in dichloromethane solution (crystals of this compound suitable for X-ray diffraction could unfortunately not be obtained). Its 31PN M R and UV spectra are identical with those of a mixture of t r ~ n s - P t I ~ ( P Mand e ~ )PMe3 ~ (1 :1) but are different from those of [PtI(PMe3),]PF, (Figures 3 and 4). The 31P doublet and triplet are shifted to high field, and one ‘J(Pt,P) coupling constant is quite uncharacteristic of a phosphorus atom in a trans position to iodide ion in a “square-planar” environment. The NMR pattern may arise from various ideal geometries: a trigonal bipyramid with (i) one PMe, and (ii) two PMe, in axial positions or a square pyramid with (iii) one iodide ion in the apical position, (iv) one PMe3 in the apical position and two basal iodide ions in cis positions to each other, and (v) one PMe, in the apical position and two basal iodide ions trans to each other. Meakin and J e s ~ o have n ~ ~ shown in
(38) Berman, H. A.; Stengle, T. R. J . Phys. Chem. 1975, 79, 1001.
(39) Meakin, P.; Jesson, J. P. J . Am. Chem. SOC.1974, 96,5751.
I
450
400
350
300
250
-
200 A(nm)
Figure 4. UV spectra in dichloromethaneof (a) PtI,(PMe,), and (b) [PtI(PMe3)3]PF6,[Pt] = 2.58 X M.
\
PtX2(PR3)2in Presence of PR, in CH2C12
Inorganic Chemistry, Vol. 19, No. 5, 1980 1359
Table 111. 31PNMR Parameters for Tertiary Phosphine Complexes of Platinum(I1)
no. la,b
cis- and trans-PtCl,(PMe,),
2a,b
cis- and trans-PtBr,(PMe,),
3a,b 4 5 6 7 8
[PtBr(PMe,),] Br [ PtI(PMe,),] PF,d
9 10 11 12 13 14a,b
-24.9 -24 -25.1 -23.8 -27.3 -26.0 -26.9 -27.5 -26.8 -25.5 -25.6 -25.5 -26.1 -26.1 -38.2
... ... ...
...
9.0 9.3 9.9
15 16 17a,b
9.8 0.9 1.4 1.4
18 19 2Oa,b 21 22 23
1.3 12.2 18.1 18.9 -0.7
3489 3480 3439 3426 3317 3306 3370 3402 3368 3406 3412 3404 3329 3349 4082
... ...
...
... 3502 3518 3442 3499 3446 3505 3508 344 1 3459 3440 3694 3645 3641 3783
-15.8 -15.8 -21.5 -20.4 -32.3 -32.2 -12.0 -12.6 -12.0 -15.6 -16.6 -15.6 -20.3 -20.5 -30.3 -30.1 -31.8 -35.4 -21.5 12.1 12.2 11.6 17.4 4.5 4.9 10.2 10.0 18.4 29.8 29.6 19.9
I
23 86 2379 2324 2336 2236 2230 223 1 2266 2230 2233 2255 223 1 2227 2248 2164 2465 2497 2420 2230 2394 2391 2263 2233 2266 2319 23 80 2261 2266 2264 2595 2415 2410 2600
a
22b a
22b a
22b 22 23 22 22 25 24 21 21 20
a
36b$C a a
36b,C a a
36b*C a a a
a
3 9
a 24 19
a
19
a
31 a 26e 19
a
19
a
31 18 18 19
a a a a,
f
This work; in CD,Cl, at -40 "C for 4-9, at -50 "C for 10-12, and at room temperature for all other complexes. Chemical shifts are in ppm referred to external H,PO, (62.5%) and are correct to *O.l ppm; a negative sign indicates a shift to higher field relative to the reference, 'H PIP} INDOR measurements in CH,Q, referred to external H,PO, (85%). Coupling constants are in H z and are correct to r3 Hz. NO; as counterion. 6 (PF,) =-145.0 (heptet, 'J(P,F) = 712 Hz). e In CDC1,. Present together with [PtCl(P(tol),),] NO, (ratio 1 : l ) in the solution obtained by mixing 20a + P(tol), + &NO, (1 :1 :1). a
the case of five-coordinate platinum(I1)-phosphite complexes, that the 31Psignal of axial phosphites appears at higher field than that of equatorial phosphites. Moreover, Meier40 has shown in the case of NiX2L3,that the relative positions of the 31Psignals (a doublet and a triplet) are the same whether L is trimethyl phosphite or trimethylphosphine. By analogy, the triplet should appear at higher field than that of the doublet for structure i and at lower field for structure ii. In fact the triplet is centered at -38.2 ppm and the doublet at -30.3 ppm. Thus structure ii is unlikely. Structure iii is also unlikely since the presence of an iodide ion in apical position should modify both 'J(Pt,P) coupling constants with respect to those of [PtI(PMe3)3]PF6.In fact, 'J(Pt,Pl) is greater by ca. 750 Hz whereas 'J(Pt,P2) is only slightly affected (Table 111). All structures, except v, should give rise to two IR bands corresponding to the Pt-I stretch. Since only one IR and Raman absorption is present in the v(Pt-I) region (see Experimental Section), this leaves structure v as the proposed ideal structure for Pt12(PMe3)3in solution. FMel M e 3 4I ,
Pt
' I
'me3 V
The addition of 2 equiv of L to PtX2L2in dichloromethane solution gives rise to new observable species only in the case when L = PMe,. The 31PN M R spectrum of a mixture of
PtX2(PMe3)2and PMe, (1:2) at -60 "C presents a singlet (with satellites due to Pt-P coupling). This singlet could result from a fast exchange between chemically nonequivalent phosphines; however, the 31P(1HJFT NMR spectrum in CHClF2 down to -155 OC does not show any change either of the multiplicity or of the line width. Thus the species formed contain four coordinated phosphine ligands and are of C4, symmetry. These "tetrakis" species should be formulated as [PtX(PMe3)4]+(X = C1, Br, I) since their 31PNMR spectra are different from that of [Pt(PMe3)4](BF4)236and also since the chemical shift and the 'J(PfP) coupling constant change when the nature of X is varied. Moreover, [PtI(PMe3)4]+is yellow whereas [Pt(PMe3)4]2' is colorless. N o new species appear on adding a large excess of phosphine to PtX2L2; however, when the temperature is raised, a fast exchange of phosphine is observed in the case of [PtCl(PMe,),]+ and PMe3 (vide infra). 2. Crystal Structure of [PtCl(PMe3)3]CI. White needles of [PtCl(PMe,),]Cl were grown by slow evaporation of a (1:1.2) in dichloromixture of c i ~ - P t C l ~ ( P M and e ~ ) PMe3 ~ methane-benzene under argon. All crystals were twinned; however, part of a single domaine was cleaved from a large needle. X-ray measurements were carried out with a Syntex P21 automatic four-circle diffractometer. The crystal data and the methods used for intensity collection, structure solution, and refinement are summarized in Table IV. The crystal form was accurately measured as before4I and used to correct the (41)
(40)
Meier, P. Thbe de doctorat, Universitt de Lausanne, 1978.
Pinkerton, A. A.; Carrupt, P. A.; Vogel, P.; Boschi, T.; Nguyen, Thuy Hai; Roulet, R. Inorg. Chim. Acta 1978, 28, 123.
1360 Inorganic Chemistry, Vol. 19, No. 5, 1980
Favez et al.
Table IV. Summary of Crystal Data, Intensity Collection, and Refinement formula mol wt dimens, mm cryst class a, A
b, A c, A
P , deg
v, A' 2 dcalcd, g/cm3 FOOO
space group systematic absences
[PtCI(PMe3),]C1 453.61 0.05 X 0.1OX 0.38 monoclinic 29.468 (3) 11.032 (2) 10.709 (1) 100.589 (8) 3422.1 (7) 8 1.76 1904 c2/c hkl: h + k = 2n + 1 h01:1=2n+l
radiation
Mo Ka, Nb fdtered (h = 0.710 69 A)
p, cm-'
91.9 28-8 scan profile i n t e r p r e t a t i ~ n ~ ~ 0.40 h, k > 0, * I 2252 301 16.6
scan method bkgd source ((sin e)/h)max data collected no. of unique reflctns no. of reflctns > PEt3 (0.039)> P(tol), (0.016). The trans effect of a phosphine being greater than that of C1-, the displacement of C1 by L from trans-PtC12L2must be slower than from cis-PtC12L2. Likewise the displacement of L trans to C1 in [PtClL,]' by C1- must be slower than that of L trans to L. This means that the ratedetermining step for the isomerization is given by eq 11. An argument that has been used against the double displacement is the inability of C1to displace L from [PtC1L3]+.This is in fact not so, at least in dichloromethane, as shown in Figure 10. Indeed, the ,lP(lH) FT NMR spectrum of a solution of [PtCl(P-nBu,)~]C104shows the appearance of ~is-PtCl~(P-n-Bu,)~ when 1 equiv of [AsPh4]C1is added. If the double displacement is operative, reaction 12 must be a fast process compared to cis-trans equilibration; i.e., addition of C1- to [PtClL,]+ must yield initially a higher proportion of cis-PtC12L2than that corresponding to the cis-trans isomerization equilibrium. This cannot be proved in the case L = P-n-Bu3where the various reactions are too fast to follow by NMR but is best shown in the case of [Pt(CH2CN)(PPh3),]+where the rate of approach to equilibrium allows the direct observation of both isomers by ,*P NMR. C ~ ~ - P ~ C ~ ( C H ~ C N )isomerizes ( P P ~ , ) slowly ~ ~ to the trans isomer. The reaction is catalyzed by free PPh3, and the observed rate law is first order in PPh, with ki = 2.3 X lo4 M-l s-l and Klo = 0.25 at 21 OC. The complex [Pt(CH2CN)(PPh3)3]C1is not observed in solutions of the cis isomer con(54) Ros, R.; Renaud, J.; Roulet, R. Helu. Chim. Acta 1975, 58, 133.
1364 Inorganic Chemistry, Vol. 19, No. 5, 1980
Favez et al.
k
I I
I
a)
L 1
.loo
l0
30
i0
Ib
40
+M)
'20
0
-20
-40
-MI pprn
Figure 11. 31P('H)FT NMR spectra in CD2C12at 30 OC of (a) cis-PtC1(CH2CN)(PPh,)2, (b) [Pt(CH2CN)(PPh3)3]C104and [AsPh4]C1(1:l) before cis F? trans equilibration,and (c) same mixture at equilibrium.
Ii 5b
40
Ib
0
$0
-3b
40
ppm
Figure 10. ,lP{lH) FT NMR spectra in CD2C12at 30 OC of (a) ci~-PtCl~(P-n-Bu~)~, (b) [P~CI(P-~-BU,)~]CIO~ and [AsPh4]C1(l:l), and (c) trans-PtCI2(P-n-Bu,)2.
ri 1
1
Scheme I t r a n s -F tY,:L2
c/s- P t X 2 L Z
L
L
I
I
L-Pt-L
+
YL
4 X
taining an excess of PPh,; however, we were able to prepare Its 31P(1HJ FT and characterize [Pt(CH2CN)(PPh3)3]BF4.54 N M R spectrum shows an AX, pattern with a triplet (1:2:1) for the phosphorus atom P1 trans to the alkyl group and a doublet twice an intense for the two phosphorus atoms P2trans to each other. The complex is stable in dichloromethane but addition of a stoichiometric amount of [AsPh4]C1 rapidly yields cis-PtC1(CH2CN)(PPh3), (Figure 11). As this substitution liberates triphenylphosphine, the PPh,-catalyzed isomerization then proceeds until the cis-trans equlibrium is reached. Recently L O U W 'suggested ~ an alternative mechanism (Scheme I) where isomerization proceeds via the pseudorotation A & B. Even though we did not observe species such as PtC12L3in solution, the equilibrium (1 3) must take place [PtXL,]+ + x- PtX2L3 (13)
*
in solution. Both species are definitively present in dichloromethane solution in the case X = I and L = PMe, as shown in Figure 12. The addition of increasing amounts of [NBu4]I to [PtI(PMe3),]PF6 gradually shifts the 31P(1H]FT NMR spectrum to that of Pt12(PMe3)3,the equilibrium constant of reaction 13 being 340 f 40 M-l at -60 "C. It should however
Figure 12. 31P{1H) FT NMR spectra in CD2CI2at -60 OC of (a) Pt12(PMe3),, (b) [PtI(PMe3),]PFs and [NBu4]I (l:l), and (c) [PtI( PMe3)3]PFs.
be noted that even though the exchange of phosphine is blocked at that temperature, a fast exchange of I- ion must still be taking place between the four- and five-coordinate complexes since only one doublet and one triplet are observed (Figure 12b). We have seen in the two limiting cases above that, for X = C1 where the observed species is [PtC1(PMe3)J+ and for X = I where Pt12(PMe3), is now observed, no evidence for an intramolecular process of the type A P B could be found. The fastest process in each case is the intermolecular phosphine exchange through equilibriums 7 and 9, respectively. English, Meakin, and J e ~ s o n have , ~ also shown that ligand dissociation from [PtHL4]+(L = PEt,) is rapid relative to the rate of intramolecular rearrangement of [PtHL,]', and we find the same trend for [PtCl(PMe3)4]+. In conclusion, all the experimental results presented in this work are in agreement with the double-displacement mechanism (a) for cis-trans isomerization at platinum(I1) in dichloromethane solution.
Inorganic Chemistry, Vol. 19, No. 5, 1980 1365
PtX2(PR3)2in Presence of PR3 in CH2Clz
Experimental Section Spectroscopic Measurements. Variable-temperature ,IP( 'H) FT NMR spectra were recorded at 36.43 MHz by using a Bruker HX-90 spectrometer equipped with a B-SW 3PM pulser, a B-SV 3B proton noise decoupler, a B-ST 100/700 temperature regulating unit, and a Nicolet BNC-12 data system. The spectra at -150 OC were obtained at 24.28 MHz by using a Bruker WP-60 spectrometer with multinuclei facilities. Field frequency stabilization was achieved on an internal 2D signal at 21.14 kG and on an external I9F signal at 14.09 kG. The temperature of the sample was measured before and after each spectrum by the method of substitution with a Pt resistance (100 a) coupled with a temperature measurement unit, Hewlett-Packard 2802-A.55 As ,IP chemical shift reference at low temperature, we used pure PEt3 in a capillary. The chemical shift of PEt3 being temperature dependent (-0.03 ppm/K), we used the plot established by Meierqoshowing the chemical shift difference between PEt3 and 62.5% H3P04 (eutectic) as a function of temperature. At room temperature, we used 62.5% H3PO4 in a capillary. All chemical shifts are reported with respect to 62.5% H3P04 with downfield shifts considered positive. The solid complexes, PPh, and P(tol),, were weighed in a nitrogen atmosphere glovebox (KSE) directly into 10-mm N M R tubes (Wilmad). Dichloromethane-d2 (CEA, France) and chlorodifluoromethane (Freon 22, Du Pont) were deoxygenated in an all-glass-Teflon vacuum line by the freeze-pump-thaw technique. The solvents and volatile phosphines were vacuum distilled on the solid samples, and all tubes were sealed under vacuum and stored in liquid nitrogen. UV spectra in dichloromethane were measured with a Beckman Acta V spectrophotometer, IR spectra with a Perkin-Elmer 577 spectrophotometerand a Bruker interferometer IFS-l13C, and Raman spectra of powdered samples with a Spex Compact 1403 equipped with a Krypton laser (647 nm). Isomerization Kinetic Measurements. (a) For PtClzL2 (L = PEt,, P(tol),), the approach to equilibrium was followed spectrophotometrically at 20 "C in the direction trans cis. The evolution of the UV spectrum of a 3.26 X 10" M solution of tr~ns-PtCl~(P(to1)~)~ (kmx = 287 nm with e = 31 800 M-I cm-') and excess P(t01)~,in CH2C12showed an isosbestic point at 272 nm. The concentration of P(tol), was varied from 9 X lod to 2.25 X lo4 M, and the variation in absorbance was followed at 287 nm. The isomerization of truns-PtClz(PEt3), (A- = 247 nm, e = 9720 M-I cm-l; 267 nm, 9820 M-' cm-l) was faster and followed at 267 nm ([PtJo= 9.7 X M; [PEt,], = 2.84 to 5.7 X M). The observed rate constant kOw was obtained as the slope of In [ODo- OD,/(OD, - OD,)] vs. t. The second-order rate constants ki and ki (eq 10) were obtained from the slope of kw vs. [L] and the value of KID In all cases, alignment coefficients were equal to or greater than 0.999. (b) For PtCl(CHzCN)L2(L = PPh,), the approach to equilibrium was followed by NMR at 21 "C in the direction cis -+ trans by integration of the undecoupled resonances of each isomer at various intervals of time and at equilibrium in the presence of different amounts of PPh, (for the trans isomer, 6(P) = 24.0; for the cis isomer, 6(P) = 20.0 and 16.8). Preparation of Complexes. All reactions were carried out in an atmosphere of nitrogen. Solvents and volatile tertiary phosphines were
-
( 5 5 ) Ammann, C.; Meier, P.; Merbach, A. E., submitted for publication.
transferred on vacuum lines. Trimethylpho~phine~~ and the following complexes were prepared as reported in the literature: la,b, 2a,b, 3a,b, 2Oa,b;I9 14a,b;5717a,b;254, 6, 8, 13;2015, 18, 21;35cis- and truns-PtC1(CHzCN)(PH3)z and [Pt(CH2CN)(PPh3)3]BF4.54 E. Manzer (Mikrolabor, ETH Zurich) carried out the microanalyses. For [PtCl(PMe3)3]Cl(5), 1 equiv of PMe, was transferred into (1 g) in acetone (40 mL) and a degassed solution of ci~-PtCl~(PMe,)~ the mixture stirred at room temperature for 10 min. A white powder precipitated on evaporating the solvent and was recrystallized from CH2C12-benzene;yield 85%. Anal. Calcd for C9H2,C12P3Pt:C, 21.87; H, 5.51; P, 18.80. Found: C, 21.97; H, 5.64; P, 18.56. IR (Nujol): 300 cm-' (v(Pt-Cl)). UV (dichloromethane): 238 nm (e 9700 M-' cm-I), 258 sh (2000). The same method was used for [PtBr(PMe3),1Br (7) and Pt12(PMe3),(9), starting with 2a and 3b, respectively; yields 90 and 75%. Compound 7 formed as white crystals. Anal. Calcd for C9H27Br2P3Pt:C, 18.54; H, 4.67; P, 15.93. Found: C, 18.20; H, 4.41; P, 15.68. IR (Nujol): 205 cm-' (u(Pt-Br)). UV (dichloromethane): 240 (sh) nm (E 9000 M-l cm-') (identical with spectrum of 6). Compound 9 appeared as air- and light-sensitive orange needles, mp 207-209 OC dec. Anal. Calcd for C9H2712P3Pt:C, 15.96; H, 4.02; P, 13.72. Found: C, 16.23; H, 4.00; P, 13.81. IR: 148 cm-' (v(Pt-I)). Raman: 146 cm-l (v(Pt-I)). This IR band appears at 153 cm-' for 8. UV (dichloromethane): 248 nm (e 25 580 M-' cm-l), 298 (16670), 364 (5430). This UV spectrum is different from that of 8: 249 nm (e 31 280 M-' cm-'), 278 sh (15390), 334 sh (5560). Complexes 10-12, 22, and 23 were observed in solution only. Complexes 16 and 19 have the same spectral properties as those of 15 and 18,,' respectively. The 35Cl FT NMR spectrum of 420 was recorded on a Bruker WP-60 spectrometer at 5.88 MHz with quadrature detection (time pulse 20 ps; spectrum with width 5000 Hz; 4096 points; 2D lock). A line width of 4 Hz was found for its C104 signal, and a width of 3 Hz was found for NaC104 in D20.
Acknowledgment. We thank the Swiss National Science Foundation for financial support (Grant No 2.037-0.78) and Mrs. Michgle Dartiguenave (UniversitC P. Sabatier, Laboratoire de Chimie de Coordination du CNRS, Toulouse, France) for a gift of trimethylphosphine. Registry No. la, 15630-86-1; lb, 21545-76-6; 2a, 15703-02-3;2b, 23627-37-4; 3a, 15703-03-4; 3b, 21258-95-7; 4, 72778-74-6; 5, 72778-75-1; 6, 72778-76-8; 7, 72178-17-9; 8, 72778-78-0; 9, 72778-79-1; 10, 72778-80-4; 11, 72778-81-5; 12, 72778-82-6; 13, 21556-14-9; 14a, 15692-07-6; 14b, 13965-02-1; 15, 22854-50-8; 16, 72778-83-7; 17a, 15390-92-8; 17b, 15391-01-2; 18, 72178-85-9; 19, 72778-86-0; 20a, 31 173-67-8; 20b, 31 173-67-8; 21, 72778-88-2; 22, 72784-65-7; 23,72778-89-3; cis-PtC1(CH2CN)(PPhJ2, 53702-17-3; truns-PtCI(CH2CN)(PPh,),, 4248 1-62-9; [Pt(CH2CN)(PPh3)3] BF4, 55641-50-4; [Pt(CHzCN)(PPh3)JC10,, 72778-90-6. Supplementary Material Available: A listing of structure factor amplitudes (9 pages). Ordering information is given on any current masthead page. ~~~~
~
(56) Wolfsberger, W.; Schmidbaur, H. Synth. Inorg. Met.-Org. Chem. 1974, 4, 149. ( 5 7 ) Inorg. Synth. 1970, 12, 21.
